In recent years, a large number of vehicles are equipped with a vehicle door remote locking and unlocking control system. The vehicle door remote locking and unlocking control system conducts wireless communication between a vehicle wireless key (electronic wireless key: mobile device) which is carried by a user (driver) and a vehicle electronic control unit (ECU) to lock or unlock a door. This system is known as a smart key system (e.g., JP 2005-264660A).
The smart key system periodically polls the wireless key through the wireless communication from an in-vehicle device, so that the wireless key transmits a signal such as an ID code to the in-vehicle device in response to the polling, to thereby authenticate a regular user.
In this smart key system, the wireless key needs to be held in a reception standby state in such a manner that a receiver circuit of the wireless key can always receive periodic polling signals from the in-vehicle device. A power supply of the receiver circuit is normally provided by a built-in dry battery, and hence the built-in battery is liable to run down easily because of always holding the reception standby state. For example, when a vehicle is placed in storage for a long period of time in shipment, or shipping is continued several days, it is understood that polling of the wireless key is not executed for a long period of time. However, because the reception standby state continues in that state, there is the possibility that a battery lifetime of the wireless key ends unexpectedly early after the vehicle has been delivered to the user, and the wireless key cannot be used. Also, when the receiver circuit malfunctions due to a noise of an electric appliance, the battery consumption is further accelerated because the power consumption at the time of the reception is large.
The above situation is similarly applicable to a spare wireless key that is delivered to the user as a spare key. That is, although the spare wireless key is normally carried by the user but kept at home, and is hardly used, a receiver circuit of the spare wireless key is held in the reception standby state where the battery gradually lose power. Also, malfunction occurs due to noises. Under the circumstances, there is a case in which the battery power has been exhausted when the power is actually required.
The power consumption of the wireless key that is used by a normal user is larger at the time of getting on or off the vehicle because of a polling response. However, a period of time required for the polling response communication at the time of getting on or off the vehicle and the number of times of the polling response communication per day are limited. As a result, most of the battery power is consumed in the reception standby state in the case of the constantly used wireless key. Accordingly, when the constantly used wireless key and the spare key are delivered to the user at the same time, there are many cases in which the battery power of the spare wireless key is naturally nearly exhausted when the battery lifetime of the constantly used wireless key is ended. Since the self-discharge of the dry battery is liable to be influenced by the storage temperature, the battery lifetime of the spare wireless key might have been already exhausted depending on the storage state. As a result, when the battery of the constantly used wireless key is exhausted and cannot be used, the battery of the spare wireless key is also exhausted with the result that a role as “spare” is not exerted.
The similar problem will also arise if a similar wireless key is applied to a door remote locking and unlocking control system for various subject bodies such as houses and buildings.